1. Field of the Invention
The present invention relates to a thermal transfer printer for thermally transferring an ink applied on an ink ribbon on a recording paper.
2. Description of Related Art
Conventionally, in thermal transfer printers, to inform the user of the need for changing an ink ribbon soon, various mechanisms for detecting residual quantity of the ink ribbon have been studied. For example, a thermal transfer printer in which residual quantity of the ink ribbon is calculated by measuring the outer diameter of a feed roll has been proposed. A thermal transfer printer in which residual quantity data indicating residual quantity is formed on the ink ribbon in advance and the residual quantity data is read by an optical sensor or the like has been also proposed.
However, since thickness of the ink ribbon is very thin in the thermal transfer printer in which the outer diameter of the feed roll is measured, an error of the residual quantity calculated based on the outer diameter becomes large and thus residual quantity cannot be calculated accurately. Furthermore, the printer in which the residual quantity data formed on the ink ribbon is read has a problem of causing increase in cost of the ink ribbon.
Thus, as distinct from the above-mentioned thermal transfer printers, a thermal transfer printer in which the number of revolutions of a feed roll or take-up roller is counted by an encoder attached to an revolving shaft of the feed roll or take-up roller and residual quantity of the ink ribbon is calculated based on the accumulated number of revolutions has been put to practical use. In such thermal transfer printer, however, for example, when the ink ribbon is detached after printing images several times and replaced with another used ink ribbon, residual quantity of the ink ribbon cannot be grasped accurately. Alternatively, when the ink ribbon intentionally wound back by the user is loaded, the start of an unused region cannot be located and thus printing is performed by using a region already used for printing. As a result, normal printing cannot be ensured.
In another known thermal transfer printer, a transparent heat-sensitive zone is provided at the ink ribbon and use of an ink ribbon having a different color reproduction property can be prevented by deciding presence or absence of a discrimination mark formed on the transparent heat-sensitive zone (see Japanese Laid-Open Patent Publication No. 2000-263905, for example). In such a thermal transfer printer, provision of the transparent heat-sensitive zone in the ink ribbon necessarily causes increase in cost of the ink ribbon.